Impact clutch



' June 9 1942.

' A. AMTSBERG 2,285,639

IMPACT CLUTCH Filed July 5, 1941 2 Sheets-Sheet 2 ATTORNEY Patented June9, 1942 Y i FFlCE mrAo'r ow'ron Lester A. Amtsberg, Cleveland, Ohio,assignor to Chicago Pneumatic Tool Company, New York,

N. Y., a corporation of New Jersey Application July 3, 1941, Serial No.400,895 12 Claims. Cl.'192-30.5)

This invention relates to impact clutches by means of which a successionof rotational hammer blows may be imparted through an anvil to a drivenmember such as a nut or bolt which offers considerable resistance torotation. It is concerned particularly with the type of impact clutchwhich comprises pivotally mounted hammer dogs driven by a force whichhas a component tending to rock the dog toward releasing position. Aclutch of' this type is disclosed in applicants co-pending application,Serial No. 305,708, filed November 22, 1939, which contains genericclaims covering the present clutch.

An object of the invention is to prolong the usefulness of the clutchparts by reducing wear, particularly between elements tending to berubbed together under great pressure. Other objects are to strengthenthe parts that are susceptible t0. breakage, and to provide a moreefli-' cient distribution of forces.

A feature of the invention is a novel form of connection between thehammer dog and its associated driving cam, which allows a reduction inthe moment of the declutching force on the dog.

Another feature resides in the novel shape of the impactsurfaces on thehammer dogs and as sociatedanvil, which permits release in response tothe reduced declutching moment and which results in efiicient operationunder varied conditions.

Another feature is an auxiliary drive between the driving cam and thehammer carrier which limits angular movement of the cam relative to thehammer assembly and prevents drag in of the dogs over the anvil duringthe first 90 degrees of lost-motion of the hammer assembly.

Other objects and features will appear from the description whichfollows.

In the accompanying drawings, which illustrate one embodiment of theinvention:

Fig. l is a longitudinal section of an impact wrench, the grip handleand motor housing being shown partly in elevation and the upper end ofthe handle being broken away;

Fig. 2 is a cross section, as indicated by the arrows 2 in Fig. 1,showing the clutch hammer dogs i and the means for pivotally carryingthem;

Fig. 3 is a side elevation of a part of the wrench a fragmentary portionof the associated driving cam being illustrated in broken lines;

Fig. 5 is a side elevation of the clutch hammer dog shown in Fig. 4,looking away from the axis 01' revolution of the clutch;

Fig. 6 is a side elevation of the rear portion of the tool head 'oranvil;

Fig. 7 is a cross section through the hammer dogs and anvil, asindicated by the arrows I in Fig. l, the clutch housing being omitted,the dogs being shown in the position they assume immediately followingtheir release from the impact shoulders on the anvil;

Fig. 8 is a view similar to Fig. '7 but with the dogs advanced degrees;

Fig. 9 is a view similar to Fig. 7 with the dogs advanced an additional90 degrees and at the instant of delivery of an impact;

Fig. 10 is a cross section through the hammer dogs and driving cam asindicated by the arrows m in Fig. 1, theclutch housing being omitted,the hammer dogs being shown in the same posi tion as in Fig. '7; and

Figs. 11 and 12 are views similar to Fig. 10 but with the position ofthe dogs corresponding to Figs. 8 and 9 respectively.

In Fig. 7 and in Fig. 8, the illustration of the hammer dogs in brokenlines is 90 degrees ahead of the position shown in full lines in thesame figure. The principal parts of the illustrative clutch are enclosedwithin a clutch housing is. shown in Fig. 1. This housing is detachablysecured in fixed relation to a motor housing 20 and a pistol grip handle2| by any suitable means such as the usual arrangement of bolts andflanges (not shown)... The front end of the clutch housing is taperedand fluted at 22 to provide another grip portion.

A reversible air motor 23 within the motor housing includes a cylinderor cylinder liner 24 the ends of which abut against end plates 25. Therear end plate has a fiange 26 fitting a recess in the handle member 2|and a peripheral portion fitting the motor housing 2!]. Flange 26surrounds and supports a ball bearing 21 held between end plate 25 andgrip handle 2|. A similar ball bearing 28 is mounted in a flange,projecting forwardly from the front end plate 25. Ball bearings 21 and28 respectively support rear and front shafts 29 and 30 integral withand projecting from a rotor 3|. The rotor'is of cylindrical shape and isarranged coaxially with its shaft and with the clutch housing ill buteccentric with the cyllnder 24 to provide a crescent shaped chamberbetween the rotor and cylinder, The rotor is provided with a pluralityof radial slots in which blades 32 are mounted for movement with theirouter edges in scraping contact with the cylinder to divide the crescentshaped chamber into a series of pockets between the inlet and exhaustends. A reverse lever 33 controls the direction of flow of compressedair and hence the direction of rotation of motor 23. For a furtherdescription of one form of motor which may be employed to drive theclutch of the present invention, reference is made to Amtsberg UnitedStates Patent 2,077,733, April 20, 1937.

Positioned centrally of the clutch housing is a rotatable tool head ordriven spindle 35 having an elongated shank 36 and having an anvilportion comprising jaws 31 adapted to receive rotational impacts ashereinafter described. Under the usual operating conditions theseimpacts tend to misalign the tool head axis, as it is practicallyimpossible to manufacture an impact clutch in which both anvil jaws arealways struck with the same force at exactly the same instant. Shank 36of the tool head is supported with a rotating fit in a steel bushing 39.A resilient sleeve 40 made of oil resisting rubber surrounds the bushingand is vulcanized to the outer surface thereof. A synthetic rubber-likematerial known to the trade as Neoprene is suitable for this pur pose.The synthetic rubber sleeve 40 has a press fit with a counterbore 4!near the front'end of clutch housing I3 and the lower end of the sleeverests on a shoulder extending between the counterbore and-a bore 42. Thebore last mentioned is slightly larger in diameter than the steelbushing 33 and in operation metal-to-metal contact between the bushingand housing is avoided.- The upper end of the resilient sleeveterminates at an annular flange 43 supporting a similar flange on thesteel bushing and seated on a shoulder of the clutch housing.

The rear end of the tool head 35 is supported in axial alignment withthe steel bushing 39 and with rotor shaft 30 by means which include apilot shaft 49 seated in complementary recesses in the rotor shaft 30and tool head.

The hammer assembly surrounds the anvil and extends between twosimilarly constructed end lates which constitute carriers by which theassembly is revolubly supported. Rear carrier 50 is mounted foroscillatory movement about a bearing surface provided on the rear end ofa driving cam splined to the rotor driving shaft 30. A bearing spacer 52abuts against the rotor bearing 28 at its rear end and the driving cam51 and hammer carrier 50 at its front end to secure the cam and carrieragainst rearward axial movement. A thrust plate 53 surrounding the pilotshaft 49 engages the front end of the driving cam and the rear face ofthe tool head 35 permitting relative rotation therebetween. Forwardmovement of the carrier 56 is prevented by engagement with projectionsradiating from the front end of the cam 5| and to be describedhereinafter. The front end plate or front carrier 55 for the hammerassembly is mounted for rotary movement relative to the shank 36 of thetool head 35, a bushing 56 being interposed between the carrier and thetool head. The bushing 56 and front carrier 55 abut against a shankspacer 51 and against a thrust washer 58. The shank spacer engages thefront of the anvil jaws 31 while the thrust washer seats on the steelbushing 33 whereby the tool head 35 and carriers 50 and 55 are supportedagainst axial thrusts.

A pair of heavy hammer dogs 66, similarly constructed and arranged, aresupported for oscilaesaese latory movement about pivot pins 6| whichextend through openings in the dogs and carriers, the heads of the pivotpins being retained by the thrust washer 58. A pair of bolts 62 arearranged to pass through openings in the carrier plates and each bolt issurrounded by a spacer sleeve 63 whose ends abut against the carrierplates. The bolts and pivot pins are evenly spaced about the axis ofrevolution, as illustrated in Fig. 2 and extend parallel to the axis ofrevolution and cooperate with each other to hold the carriers rigidly infixed relation to each other and to the pivot pins.

The hammer dogs 60 are capable of delivering torsional impulses to thetool head far in excess of the maximum torque of the motor 23 withoutresorting to reduction gearing, resilient power accumulators or springoperated clutching mechanism. The hammer dogs are positively guided,after their release from driving relation with the anvil, bycomplementary surfaces on the dogs and anvil until the striking surfaceon the hammer dog is properly oriented into the annular path of thestricken surface on the anvil. The impact surfaces are held inengagement until revolution of the hammer assembly has been arrested(relative to the anvil) and the full momentum of the hammer transferredto the anvil as a rotational hammer blow. Upon termination of the blowthe hammer dogs are automatically declutched by a novel mechanismincluding a set of cams between the rotor shaft and the hammer dogs,which will be described hereinafter. The declutching mechanism isdesigned with a view toward delaying its effectiveness until the contactpressure between the hammer and anvil has been reduced in order to avoidrapid wear that would otherwise result from the rubbing action of theimpact surfaces during the concurrent delivery of a blow and movement ofthe striking surface toward declutched position. v

The reclutching mechanism comprises an internal cam surface 65 on thedog 60, having the general shape of a sector of a cylinder whose centerlies on the near side of the axis of revolution of the clutch. Thisinternal cam cooperates with the anvil jaw 31, the periphery of which isa flat surface rounded at the corners and the sides of which constituteimpact receiving shoulders or stricken surfaces 61 extending in anapproximately radial direction.

Anvil shoulders 61 are driven, sometimes continuously and at other timeswith a succession of hammer blows, by the impact shoulders 68 which areautomatically movable into and out of 'the annular path of shoulders 61.The anvil or tool head 35 also has a'pair of cylindrical surfaces 66intermediate the jaws 31. Surfaces 66 are concentric with respect to theaxis of rotation, and complement the jaws in guiding the dogs 60 whilethey are rotating ahead of the anvil.

In accordance with a feature of the present invention, the strickensurfaces 61, as well as the striking surfaces 68 at the opposite ends ofthe dogs 66, are cylindrical. At the time of impact, these cylindricalsurfaces are arranged to coincide with the are 69 (Fig. 9) which isconcentric with the pivot pin 6|. This permits'the dog to rock about thepivot in the declutching direction without being required to displacepivot 6| relative to the anvil.

Figs. 7, 8 and 9 show how the dog 60 is rocked from one extreme positionto the other in a reclutching direction, or clockwise about pivot 6|, asit revolves through degrees, or one cycle,

in a clockwise direction about the axis of the anvil 35. Referring toFig. 7. which shows the hammer dog 60 just'after it has been declutched,the trailing end of the internal cam 65 rides over or passes near thecylindrical surface 66 without causing any substantial movement in areclutching direction as the dog moves from the full line to the dottedline position shown in this re. Thereafter the inner cam surface 65engages the anvil jaw 31 and due to the eccentricity of surface 66 thedog is caused to rock in a reclutching direction. Fig. 8 shows in fulllines the position of the dog after 90 degrees of rotation ahead of theanvil and it will be seen that the dog is rocked halfway towardreclutching position. The broken line illustration in Fig. 8 shows thetrailing end of the internal cam 65 rubbing over the flat peripheralface of the anvil jaw 31. The dog completes its reclutching or rockingmovement shortly prior to the re-engagement of the impact surfaces 61and 68 and these surfaces are in complete registry at the time ofimpact. Just before the blow is struck the dog remains at the extremityof its rocking movement due to its inertia and friction. As anadditional safeguard against accidental displacement of the hammer dog,it may be so mounted that the center of gravity of the weight 68 isofiset slightly inward of the center of the pivot 6 I. Thus mounted, theweight is dynamically unstable and tends to remain at one extremity orthe other of its rocking movement.

A novel mechanism is provided for declutching I the hammer dog 60automatically upon termination of the hammer blow delivered between theimpact shoulders 68 and 61. In accordance with this invention, thedeclutching mechanism comprises a central projection II at one end ofeach of the dogs 68. Driving cam 5| has a pair of projections 12 foreach of the associated dogs 60, said projections defining a slot 13therebetween. Preferably, the driving cam 5| is so designed that I theside walls of slot 13 are parallel, whereby to facilitate the cutting ofthe slot by a milling operation. Near the open end of the slot, eachside wall is cut on a radius of about a quarter inch, the roundedportion providing a cam driving shoulder H. The cam shoulder 14 impartsforce to the dog 68 along a line 15 (see Figs. 10 and 12) inward of thepivot pin 6|, thereby tending to rock the dog in a counter-clockwise ordeclutching direction. This rocking component of motion becomeseffective to move the clutch dogs from the engaged position of Figs. 9and 12 to the released position of Figs. 7 and 10 when the pressure ofstriking surface 68 against stricken surface 6! is 'suiiiciently reducedto permit relative rubbing action between said surfaces.

Another feature of the present invention re- I sides in a supplementarydriving connection between the driving cam 5| and the hammer assembly. Acomparison between Figs. 12 and 10 shows that the declutching movementof the dogs 68 is accompanied by a slight rotation of the and longerlife of the parts which otherwise would be subjected toa rubbing action.

Preferably the shank -36 of tool head 35 is of sufllcient axial lengththat advantage may be taken; of the torsional elasticity of the steel.Thus, whena rotational hammenblow is delivered to the rear end of thetool head and the front end is held in engagement with a frozen nut N,the tool head twists slightly. Upon termination of the impact, the shankunwinds causing the hammer dogs 60, carrier members 58, 65

and 6!, driving cam 5| and rotor 3| to rebound as a unit in a directionopposite to the rotary impact. The rebound acts to momentarily relievethe contact pressure between the impact surfaces 61 and 68 therebyfacilitating declutching and reducing the rubbing action of the impactshoulders 61 and 68 on each other.

The front end of the shank 36terminates at a socket engaging projection19 of polygonal cross section fitting a correspondingly shaped openingin wrench socket 811 for the driven bolt or nut N. The end of the toolhead and the socket have registering transverse apertures 8| and 82which receive a locking pin 83. The pin is preferably a rigidcylindrical rod and serves to prevent accidental detachment of thesocket from the tool head projection 19, but permits ready removal andreplacement of the socket when that is desired. The locking pin issecured by means of an elastic retainer ring, such as rubber band 86,surrounding the pin and seated in an annular groove 81 on the socketmember 80.

Briefly summarizing the operation of the illustrative embodiment of theinvention let it be assumed that the operator has manipulated thethrottle lever (not shown) and reverse lever 33 to admit air to themotor 23 to drive the socket in a clockwise direction, looking forward.shoulder 14 on the driving cam 5| pressesagainst the hammer dog 68 insuch a direction that the dog has imparted to it a motion of revolutionabout the axis of tool head 35 and 'a component of forc which tends todeclutch it relative to the anvil jaws 31 on the tool head. The dogs arepivotally mounted on a carrier assembly which includes the carrierplates 50 and 55 and the pivot pins BI and this assembly is carried withthe dogs as they revolve. At times the driving force is supplemented bydriving shoulders 11 acting direct against the spacer sleeves 63 withoutimparting a declutching component of force to the dogs. Assuming thatthe tool head does not immediately partake of the rotation of the hammerassembly, the movement of the dogs relative to the tool head is guidedby the cam connection 31, 65, through the positions indicated in Figs.7, 8 and 9 until the clutch becomes fully meshed, with the impactshoulders 61 and 68 contacting each other over their entire areas. Ifthe resistance to rotation of the driven nut N is relatively slight, theclutch parts may remain for an appreciable time in the Fig. 9 position,all parts revolving in unison due to inertia, centrifugal force, andfriction. As the nut N is being driven, the dog may occasionally bedeclutched to the Fig. 7 position and move into reengagement with animpact. While it is desirable to minimize impacting during the. runningup operation on the driven nut, such action is not regarded as highlyobjectionable.

After the nut N becomes seated, the resistance to further rotation ofthe nut and consequently of the socket 88, tool head 35 and anvil jaws31, increases abruptly. The pressure of the driving cam shoulder llagainst the hammer dog 60, which is represented by the arrow 15 in Fig.12 increases with the torque requirement and, when the moment of itsforce about the pivotal axis 6| overcomes the opposing forces the clutchdisengages to the position of Figs. 7 and 10, the dog 60 being moved toits extreme counter-clockwise position relative to pivot 6|.

Immediately following the release of the ham mer assembly from the anvilit starts to revolve clockwise, moving from the full line to the dottedline position of Fig. 7, the trailing end of the internal cam 65 beingheld in contact with, or closely adjacent to, the cylindrical anvilsurface 66 due to the declutching component imparted to the dogs 60 bythe cam driving shoulder 14. The declutching component is not effectiveto press the dog hard against the surface 66 since it is substantiallyrelieved by the auxiliary driving force transmitted between cam shoulder11 and spacer sleeve 63 which does not tend to rock the dog.Accordingly, this invention reduces the wear on the dogs and anvilduring the first part of the lost motion period of the hammer assembly.As the dog approaches the full line position of Fig. 8, it starts torock about pivot 6| due to the engagement of internal cam 65 with anviljaw 31, and the auxiliary driving shoulder 'Il ceases to be effective.Rocking movement of the dog continues as the hammer assembly revolvesand increases in angular speed as the dog passes beyond the dotted lineposition of Fig. 8 when the trailing end of the internal cam 65 runsover the flat peripheral face of the anvil jaw 31. By the time thetrailing end of the dog moves out of contact with the anvil jaw 31, ithas arrived at the extremity of its rocking movement. An instant laterthe impact shoulder 68 at the front end of the dog strikes thecorresponding shoulder 61 on the anvil jaw. The interval of time betweenthe release of the trailing end and the impact at the leading end of thedog is too short to permit any appreciable rocking movement away fromthe meshing position. Moreover, any tendency to produce such rockingmovement would be opposed by friction, inertia and centrifugal force.

It isimportant that rocking movement of the dog be prevented during thetime that the blow is delivered as otherwise the impact shoulders 68 and61 would rub. each other under very great pressure and thereby causeexcessive wear. This invention provides improved means for delaying thestart of. the rocking movement of the dog in a declutching directionuntil the full force of the blow has been delivered and the hammerassembly is brought to rest relative to the anvil.

It should be understood that the force of the blowis due to two factors:first, the transfer of kinetic energy previously stored in the hammerassembly, which includes the dogs 60, end plates 50 and 55, andassociated connecting pins and spacer sleeves; second, the driving.force bein delivered to the dog by-the cam shoulder I4 concurrentlywith the delivery of the hammer blow. The factor first mentionedaccounts for over 90 per cent. of the force of the blow and is directed,as indicated by the arrow 89 in Fig. 9, along the radius of the curvedimpact surfaces 61 and 68, whereby the greater part of the force of theblow does not set up any component tending to rock the dog. On the otherhand, the friction which it develops prevents rocking movement. Thesecond and minor factor, however, tends to rock the dog since this partof the forceis directed along the arrow 15 of Fig. 12 which is offsetfrom the pivotal axis 6|.

In accordance with this invention, the rocking component of the forcetransmitted by the cam shoulder 14 is reduced to prevent this force frombecoming effective prior to the completion of thedelivery of the hammerblow. This is accomplished by so designin the parts that the arrow 15 ismuch closer to the pivot 6| than to the center of the driving cam 5|.

After the momentum of the hammer assembly has been absorbed by theanvil, the driving force along the line 15 is effective to rock the dogto the released position shown in Figs. 7 and 10. During the declutchingmovement of the dog, the motor shaft 30 turns slightly but the carriers50 and 55 and the associated pins on the hammer assembly remainstationary. It will be noticed that the arrow 15 is somewhat closer tothe pivot 8| in Fig. 10 than in Fig. 12. This further reduces theeffectiveness of the rocking force on the dog and prevents the dogs fromdragging on the anvil during the first part of the lost motion period.As soon as the dogs are declutched, the driving unit is relieved of itsload and accelerates to accumulate kinetic energy during a half turn ofthe motor after which the driving unit is arrested with another impact.The succession of impacts is continued as long as the operator holds thewrench socket in engagement with the torque resisting nut and continuesthe supply of air to the motor. If the resistance to rotation ismoderate the dogs will be declutched before the driving unit comes to acomplete rest relative to the wrench casing i9 although the driving unitis arrested at the time of each impact relative to the tool head 35.

The rotating parts of the illustrative embodiment are all symmetricallyarranged and it will be understood without further description that thedevice will operate in the same manner for either direction of rotation.In operation the wrench will ordinarily be used more in one directionthan in the other causing the impact shoulder 68 on one side of thehammer in to wear ahead of the impact shoulder on the other side. Asshown in Fig. 5, the projection II by which the dog is driven isprovided at both ends of the hammer 60 whereby the hammer may beinverted at the time of servicing to equalize wear between impactsurfaces 68.

Comparing the present improvement with the illustrative embodiment ofapplicant's co-pending application, hereinbefore identified, thedistinguishing features in general are as follows: first, the provisionof the auxiliary driving shoulders 11 engageable with the spacer sleeves63 to reduce drag of the dogs on the anvil; second, the curved shape ofthe impact surfaces 81 and 6|; and third, the reversal of the projectionand slot connection whereby the slot 13 is provided in the driving cam5| instead of in the dog 80.

The advantage of the curved impact surfaces 61 and 68 is that thecontacting faces are always coincidental independent of small variationsin engagement caused by variations in operation and manufacture. Also,in declutching, there is no component force to overcomeas in the case ofa flat impact surface.

By providing the slot 13 in the cam 5|, instead of in the dog 60, itbecomes possible to select any desired leverage ratio between the camand dog. Accordingly, the parts may be so designed that the cam shoulder14 drives along a line (see' arrow 15) as close to the pivot 6| asdesired with:

out resulting in any structural weakness as would be the case if a deepslot were provided in the dog. With the declutching force directed closeto the pivot 6|, its turning component is reduced to the extent that itbarely overcomes friction.

Another advantage obtained in placing the slot in the cam instead of inthe dog is that the slot may be larger and the cam driving surfaces I4may be formed on alarger radius, and therefore will not readily becomeworn.

The resiliently mounted bushing 12 for the tool head shank 36, and theelastic retainer ring 86 for the locking pin 83 are claimed respectivelyin copending applications Ser. Nos. 440,173 and 440,174, filed April 23,1942, both being divisions of application Ser. No. 305,708aforementioned.

What is claimed is:

1. An impact clutch comprising a rotatable anvil having longitudinallyextending jaws, hammer dogs revoluble in a path surrounding the jaws, arevoluble carrier for the dogs, said dogs being pivotally mounted on thecarrier for limited rocking movement into and out of the path of theanvil jaws, the pivotal axes extending parallel to the axis of rotationof the anvil, means for driving the dogs, said driving means comprisinga driving cam coaxial with and adjacent one end of the anvil, said camhaving an open slot associated with each dog, the dog having a pro-=jection within said slot, the side wall of the slot engaging the dog toimpart a force thereto extending along a line slightly oifset inwardlyfrom the pivotal axis of the dog, whereby to rock it toward releasingposition when the driving cam rotates ahead of the carrier.

2. An impact clutch comprising a rotatable drive shaft, a rotatableanvil coaxial with the drive shaft and arranged with its rear faceadjacent the front face of the drive shaft, a driving cam surroundingthe drive shaft and keyed thereto, a revoluble carrier assemblysupported for rotation on the driving cam and .on the anvil and havinglongitudinal pivot pins rotatable in a path surrounding the anvil,hammer dogs pivoted on said pins and arranged to rock into and out ofclutch engaging relation with the anvil, and a driving connectionbetween the cam and the dogs, said driving connection comprising aprojection on the dog extending rearwardly of the anvil, said projectionbeing disposed between two shoulders on the driving cam, each of saidshoulders being arranged to drive one of the two. opposite sides of thedog projection, whereby the cam may drive the dog in either direction ofrotation, said shoulder being directed to impart a force along a lineslightly inward of the pivotal axis of thedog, whereby said force isresolved into a driving and a declutching component.

3. An impact clutchaccording to claim 2 which includes complementary camelements carried by the dogs and anvil for automatically rocking thedogs into the path of the anvil jaws, such rocking movement causing therotation of the carrier ahead of the driving cam.

4. An impact clutch comprising a rotatable driving cam, a coaxiallyrotatable anvil having longitudinally extending jaws arranged in frontof the cam, dogs revoluble in a path surrounding the anvil jaws, eachdog having-impact shoulders at its opposite ends engageable with andreleasable from the jaws and arranged to drive the anvil in eitherdirection of rotation, each dog being mounted on a carrier for limitedrocking movement about a pivotal axis extending parallel to the axis ofrotation of the anvil, and a driving leasing the dog from the anvil lawwhen the driving cam rotates faster than the carrier.

5. An impact clutch comprising a rotatable anvil having jaws, acoaxially rotatable hammer carrier, hammer dogs mounted on the carrierfor rocking movement into and out of the path of the anvil Jaws todeliver a series of impacts to the anvil, a driving cam imparting forceto the dogs along a line offset from the pivotal axis, whereby suchforce has a component tending to rock the dog toward clutch releasingposition, and.

means for relieving the dogs of the releasing component of force afterthey are released fromthe anvil jaws, said relieving means comprising ashoulder on the driving cam engageable with a fixed part of the hammercarrier to limit relative rotation of the driving cam with respect tothe carrier.

.6. An impact clutch comprising a revoluble hammer carrier having frontand rear end plates and connecting elements therebetween forming a asubstantially rigid structure, a coaxially rotatable anvil havinglongitudinally extending Jaws between the front and rear end plates,hammer dogs supported by the hammer carrier for limited relative pivotalmovement about respective axes parallel to the anvil, each dog having animpact shoulder positioned to be moved into and out of the circular pathof the anvil jaws in response to the pivotal movement aforesaid, adriving cam at the rear end of the anvil, said driving cam having adriving shoulder engageable with the dogs to transmit torque through thedogs to the carrier, said cam also having an auxiliary driving shoulderengageable at times with one of the connecting elements to impart torquedirect to the carrier.

7. An impact clutch according to claim 6 in which the first mentioneddriving shoulder is positioned to transmit force to the dog along a lineslightly inward of the pivotal axis of the dog,

whereby the driving cam rotates slower than the hammer carrier while thedog is being rocked into impacting relation with the anvil jaws androtates faster than the carrier while the dog is being released.

8. In an impact clutch, a hammer dog of generally arcuate shap'e, saiddog having an inner concave surface and an outer convex surface,approximately radial walls extending between said surfaces, the doghaving a bore providing a pivotal support centrally located with respectto the radial walls, front and rear end walls extending in planesperpendicular to the axis of the bore, and a projection extending beyondone of the end walls by means of which the hammer dog is adapted to bedriven.

9. A clutch comprising a driven spindle-having longitudinally extendingjaws, each provided with shoulders on its opposite sides by means ofwhich the spindle may be driven in either direction, a revolublecarrier, driving dogs each supported by the carrier for limited rockingmovement about a pivotal axis parallel to the axis of rotation of thespindle, each dog having at its opposite ends driving shoulders adaptedto be rocked into and out of the path of rotation of the jaws,automatically operable declutching means for rocking the dogs towardreleasing position while the driving shoulders are in engagement withthe driven shoulders, characterized in that the driving and drivensurfaces are in the shape of a sector of a cylinder, the axis of whichcylinder is coincident with the pivotal axis of the dog, whereby the dogmay be rocked to releasing position without displacing its pivotal axisor the associated carrier.

10. A clutch comprising a driven spindle having longitudinally extendingjaws, a revoluble carrier, driving dogs each supported by the carrierfor limited rocking movement about a pivotal axis parallel to the axisof rotation of the spindle, each dog having a driving shoulder adaptedto be rocked into and out of the path of rotation 01' the jaws,automatically operable declutching means for rocking the dogs towardreleasing position while the driving shoulders are in engagement withthe driven shoulders, characterized in that the driving and drivensurfaces are in the shape of a sector of a cylinder, the axis of whichcylinder is coincident with the pivotal axis of the dog, whereby the dogmay be rocked to releasing position without displacing its pivotal axisor the associated carrier, and whereby to prevent the reaction of theforce of the blow from rocking the dog.

11. An impact clutch comprising a revoluble hammer carrier having frontand rear end plates and connecting elements therebetween forming asubstantially rigid structure, a coaxially rotatable anvil havinglongitudinally extending Jaws between the front and rear end plates,hammer dogs supported by the hammer carrier for limited relative pivotalmovement about respective axes parallel to the anvil, each dog having animpact shoulderpositioned to be moved into and out of the circular pathof the anvil Jaws in response to the pivotal movement aforesaid, adriving cam at the rear end of the anvil, said driving cam having aradially open slot associated with each hammer dog,. the dog having aprojection extending into the slot, each 0! the opposite side walls ofthe slot having a driving shoulder engageable with the projection toimpart torque thereto, the dog being symmetrically proportioned onopposite sides of the pivotal axis for selective driving in eitherdirection of rotation. v

12. An impact clutch comprising a revoluble hammer carrier having frontand rear end plates and connecting elements therebetween forming asubstantially rigid structure, a coaxially rotatable anvil havinglongitudinally extending Jaws between the front and rear end plates,hammer dogs supported by the hammer carrier for limited relative pivotalmovement about respective axes parallel to the anvil, each dog having animpact shoulder positioned to be moved into and out of the circular pathof the anvil jaws in response to the pivotal movement aforesaid, adriving cam at the rear end of the anvil, said driving cam having aradially open slot associated with each hammer dog, the dog having aprojection extending into the slot, one of the side walls of the slothaving a driving shoulder engageable with the projection to imparttorque thereto, the pressure of the driving shoulder against the dogprojection being directed along a line slightly inward of the pivotalaxis of the dog, whereby rotation of the driving cam ahead of thecarrier rocks the dogs toward clutch releasing position.

' LESTER A. AMTSBERG.

